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STS-113 ISS and P1 Truss

Question and Answer Board

Host: When did the P1 arrive at the Kennedy Space CenterExpert: It arrived in July of 2000.Host: How long did it take to process?Expert: We turned it over for shuttle integration just this last spring so we have been working on it a little while, but it worked great.

James from Cananduagia
How hard will it be to pass the truss from the shuttle arm to the station arm?

Wow, I am impressed that our viewers know we are doing a handoff. That's great! Let me start by explaining a little bit of why we are doing a handoff. It turns out in this situation, neither the shuttle arm nor the station arm have the reach capability to take the P1 Truss out of the payload bay and attach it to S-Zero. So we are going to handoff from the shuttle arm to the station arm. As far how difficult this is, once we get the two arms in proximity of each other, it will probably take a little less than a half an hour to complete the handoff. We actually did a similar task on 6A when we handed off the Spacelab palette from the station arm to the shuttle arm. So we had a little practice.

Rick from Helena, Montana
When all of the Truss units are installed, how bright will the ISS be to us on the ground?

If you go outside at night now and it is a visible night for the entire station, you will see that next to the moon and Venus it is probably the brightest thing in the sky already and once we get the solar panel in place it will be even brighter. It's really a spectacular site to see. There are quite a few Web sites out there that can tell you how to go and see when the station will pass overhead and be visible.

Anne from Melbourne
How do the rockets on the shuttle or the ISS propel themselves in space, if space is a vacuum there is nothing to push off of?

The best way to answer this is to explain a little on how rocket engines work. To start with, rocket engines basically operate off of Newton's, I believe it's the third law -- for every action there is an equal and opposite reaction.

Pretend that you are an astronaut in space, and you have a baseball in your hand and you decide to throw the baseball, you throw it as hard as you can. What is going to happen is you are going to move backwards and the ball is going to move forward, action-reaction. The same thing is true in a rocket engine. In the baseball case, the baseball is the mass and the acceleration that you use to throw the baseball multiply times that mass and you get the force. Well, in the rocket engine the force is in the thrust and the mass for the rocket engine is actually the propellant or the fuel that gets burned, so the acceleration happens when you burn the fuel and then we expel it out the rocket nozzle at a very high velocity and that creates your thrust.

Daniel from Des Moines
When the truss structure is complete, will each part still be called by its name, or will the truss just have one name?

Actually the truss structure will just be called the truss structure. We will refer to the individual segments like S1, S0, and P1 we will continue to call by name for maintenance purposes or operations.

Host: Is there any reason they are called S1 and P1? Expert: Yeah, good question. S stands for starboard and P stands for port. They build up in numbers as you go outward. S1 is closest to the center truss, which is S-Zero, and as you go out to S3 and so on you progressively go out away from the center.

Al from Burlington, Massachusetts
Why would both CETA carts be needed on the S1, isn't the system designed to have one on each side of the Mobile Transporter? Also, isn't the MT designed to be moved while the SSRMS is mated to it? Is this a test of the MT moving over rail joints?

Well, actually nominal operation for the CETA cart would be for both of them to be on the starboard side of the MT. That is the way we designed it. Although one is launched on S1 and one is launched on P1. Why would we want them on one side or on the starboard side is when we go to change out one of our orbital replaceable units, a larger one, like say a re-supply of ammonia then we would need one CETA cart for the old ammonia tank assembly and one for the new ammonia tank so that is why we need both carts on one side.

Question: Also, isn't the Mobile Transporter designed to be moved while the SSRMS is mated to it? Is this a test of the MT moving over rail joints?

Yes, the MT is designed to move while we have the SSRMS attached to it, that is the station arm, and we do have, I believe the station arm has the capability of 11,000 lbs. As far as translating this is very exciting, this is the first time we are going to translate across the joint. When we move from worksite 4 to worksite 7 we are going to translate across from S-Zero to P1 and we need to do that because we need access to do some of the EVAs.

Sarah from Antioch
What does the P-1 truss do for the station?

Well, the P1 Truss brings up an added communication system, it also brings up the second loop of our active thermal control system, which we have another set of radiators. It also brings up another CETA cart.

PO from Silver Spring
(1)What is the P1 Truss?

Great question! And notice Tasmania. Look at all the places people are asking these questions. I love it! Well, we know absolutely, positively there is life in space. There are three people up on the space station right now. Beyond that, I don't have any conclusive evidence to say that there is, but my gut feeling is that surely with this vastness of the universe, there's bound to be life out there in unimaginable, interesting variations and I can't wait for us to find them.

Host: As Project Manager how long have you been working on the P1 and what was the most interesting part of that whole effort?Expert: About 4 years I have been Project Manager for the P1 and the Station for about 13 years. And just watching the entire Station go from the design process all the way to build to launch... it's the most exciting thing, to see a piece of hardware you worked on launch into space. It's very exciting!

Rick from Sarasota
Regarding the new truss assembly, why are they so massive? (i.e. heavy) The ISS is operating in 0-G, so there's no gravity pulling on the components; yet these trusses weigh many tons (on Earth). Why can't they be manufactured a'la the Lunar Landers that were designed to work in a low G environment?

Well, we didn't design to be heavy on purpose, and we actually tried to do just the opposite and designed it to be light as possible. The truss structure itself has to carry many electrical components that are very heavy. So we have to design a framework that can carry those loads as well as withstand the launch loads and the launch environment inside the space shuttle. When it comes to the actually weight of the truss structure it is only about one-third the fifteen tons that it weighs here on Earth. The structure itself isn't the heaviest part. We also have to make it strong enough to withstand on-orbit loads, whether we are doing operations, whether it be re-boosts or a crew member out working on the truss.

Jackie from Melbourne
Who designed the docking mechanism? Was it difficult to make sure it would work for both the Russian Soyuz and the space shuttle?

OK, lets see, the docking mechanism for the space shuttle was designed by the Russians and actually there are two different docking mechanisms. One is used for the Soyuz and Progress for the Russians. And the other is used for the space shuttle docking.

Gwen from Houston
How does the docking mechanism work? How many different areas are available for docking the shuttle?

OK for the shuttle right now we currently have three docking mechanisms on orbit, one is attached to the Russians', one is attached to the radio ports on the node and is not currently assessable in our configuration right now to dock to. And the other is attached to the lab and that is the one we will be using for mission STS-113.

Dave from Pleasantville
How does the ramp generator work inside the Rotary Joint Motor Controler?

As a matter of fact it is, the radiators on the S1 are the girls, that would be Cindy, Jan and Marsha. And the radiators on the P1 Truss are the boys, the girls did come first, and the boys are Greg, Bobby and Peter.

Question: Why were they named the Brady Bunch?

We had to get creative I guess, we had to name them for different reasons of operation and that is what we came up with.

Zethan from Omaha
In what year will the space station be completed?

The baseline right now is in January of 2008 and that would be the time frame that we would bring up the Cupola.

John and Julia from Omaha
Why is ammonia used as a coolant in the ISS truss?

Good question, actually when it comes to fluids as coolant or heat transfer fluids, water and ammonia far and away are superior to any other fluids, and we use both of them on the Station. We use water inside the pressurized modules but it does have some drawbacks and one of them would be that it freezes at 32 degrees Fahrenheit. Where as ammonia doesn't freeze until we get to minus 108 and we do see those extremes external to the pressurized modules and that is why we use ammonia.

Greg from Portsmouth
What was the biggest challenge you faced in designing the P-1 truss for the ISS?

Wow, there are a lot of challenges and I don't think I could pick the biggest challenge. Surely one of them was coordinating the large team of people involved across the country in all the sites that we worked with. Also, the launch vehicle, the space shuttle, limits us on weight so we are constantly trying to make it lighter and lighter and lighter. As well as the volume, if you take a look at the P1 Truss you'll notice it has a lot of protruding objects such as the ammonia tanks sticking out the top or the CETA carts off the bottom of the truss, so we had a set volume for the space shuttle that we have to adhere to. And probably the other thing would be that part of this truss actually rotates on orbit, so we had to figure out a way to make it not rotate here on Earth, yet make sure that the astronauts could make it rotate when they deplore our launch locks. So when we actually got it on orbit it will rotate. That was pretty complicated project.

Emilio Pérez from Lugo, Spain
In the year 2005, when the ISS is completed, will it be possible to expand the station in the future?

Well right now it is 2008 for completion but anything is possible as far as expanding in space. We are always looking at our options.

Neal from Arizona City
Will the "long spacer" be moved too when P6 is relocated?

Yes, it will. The long spacer remains attached to P6 and when we move the P6 the whole assembly goes together.

Carl from Boise
Why does the Russian made escape capsule need to be replaced periodically?

Basically what we do with things like this, is they're designed for and certified for a certain amount of on-orbit life and that is what we've got here. We've tested the systems so they are qualified for a certain period of time on orbit and in order to ensure we have a safe station, we have to bring them down and bring up a new one.

Rob from Los Angeles
What sort of issues do ground control have to deal with in holding the ISS attitude during asymmetrical phases of construction?

Wow! A little bit of background, the space station itself has an attitude envelope I'll call it, which it is required to fly in and when it is symmetrical it likes to do that just fine, but when it asymmetrical it is constantly trying to get out of that envelope. What we have is Control Moment Gyros (CMGs) that help us stay in that envelope. When we are flying asymmetrical we use a lot of the CMGs' capabilities just to stay within the envelope so when we have any disturbances, disturbances like a crew out working on the station, or doing a robotic movement with the arm, all those motivate your attitude. So we have limited capability for with the CMGs to control that when we are in an asymmetrical configuration. That makes it a tough job for the guys on the ground. They really have to monitor those operations closely when flying in an asymmetrical configuration.